The present invention generally relates to a rearview assembly and, more specifically a rearview assembly that includes a tri-band antenna module.
Vehicle communication and control systems are commercially available that provide a wide variety of communication and control functions. An example of such a system is the ONSTAR® system from General Motors Corporation. Another example of such a system is disclosed in U.S. Pat. No. 6,028,537. Each of these systems includes a cellular telephone, a vehicle position identification system (specifically GPS), a processor, and a connection to the vehicle bus. These interconnected elements not only provide for conventional hands-free telephone operation, but also enable a number of other communication operations and remote vehicle control functions. For example, such a system may automatically call 9-1-1 and transmit the vehicle location (as provided by the GPS) when the vehicle air bags inflate, enable a driver to request roadside assistance or ask for navigational directions at the touch of a button. These systems also enable remote control of vehicle functions such as remote door locking or unlocking and reprogramming/personalization of vehicle accessories. Additionally, such systems may provide for remote diagnostics of the vehicle. The systems may also allow for transmittal and reception of text/paging messages and enable the vehicle to be tracked by the owner or the police.
The ONSTAR® system has been implemented by providing an electronic module, also known and referred to as a “brick,” which incorporates most of the system electronics including the GPS receiver, the telephone circuitry, and essentially all the electrical components for the system (except for the antenna) in the vehicle trunk or under or behind the seats. The GPS microwave antenna is mounted elsewhere in the vehicle and connected to the brick by a coaxial cable. The cellular telephone antenna is typically mounted on a side window of the vehicle and is connected to the telephone receiver by a coaxial cable. The user interface, which includes a speaker, microphone, and pushbuttons, is mounted near the driver and hardwired to the brick. Additionally, the brick must be wired to the vehicle battery and/or ignition. These types of systems may also be connected to the vehicle bus (CAN, J1850, etc.), the door locks, the air bags, the vehicle radio, to any RS232, RS-422 or other serial communication ports, and to any diagnostic circuits. All this wiring makes the system difficult and expensive to implement. When offered as a dealer-installed option, the wiring complexity of the ONSTAR® system becomes even more of a problem.
Despite all the research that has been conducted and all the literature that has been generated relating to the use of position identification systems (e.g., GPS) in vehicular applications, little consideration had been given to the practicalities of where to mount the microwave antenna that is to receive the microwave signals from the satellites. The ONSTAR® system has the microwave antenna mounted behind the front windshield just beneath the headliner or on the rear deck proximate the rear windshield. This antenna mounting is described in U.S. Pat. No. 5,959,581. Installing the antenna in this position is difficult. Published International Application No. WO 97/21127 discloses the mounting of two separate microwave antennas in the two external rearview mirror housings of the vehicle. While there are two microwave antennas located in the external rearview mirror housings, the system receiver circuit is located in the interior of the vehicle. The separation of the receiver circuit from the antennas introduces significant manufacturing difficulties. Coaxial cable typically used to connect the antenna to the receiver is expensive and difficult to handle in a manufacturing process, since it cannot be kinked and is relatively difficult to terminate. Furthermore, such coaxial cable typically has relatively expensive push-on or screw-on type connectors that connect it to the system receiver circuit and/or microwave antenna. Additionally, vehicle manufacturers have expressed an unwillingness to require their assembly line workers to connect the components using such a coaxial connector.
While WO 97/21127 further suggests that the antenna could additionally be positioned within an interior mirror of the vehicle, doing so has not been preferred because the interior mirror is movable with respect to the passenger compartment, which may introduce error in the vehicle position measurements. Also, it is better to manufacture because it puts all the electronics in one housing and is more cost effective. However, it does not work as well. In general, GPS is a line of sight system. The more sky the antenna can “see,” the better the system will perform. Having the antenna mounted to the channel mount by the glass allows better visibility of the sky and hence performance. Also, it is desirable to reduce the variability inherent in the design. Having an antenna and its radiation pattern changing as different people get in the car and adjust the mirror is extremely undesirable. Further, WO 97/21127 additionally states that metallic coatings on the vehicle windshield may interfere with the operation of a receiving antenna when mounted in an interior rearview mirror assembly. Additionally, like the configuration where the receiving antennas are mounted in the two exterior mirrors, the mounting of the receiving antenna in the interior rearview mirror housing also presents manufacturing problems associated with connecting the antenna with the receiver, which apparently is mounted in the vehicle instrument panel. In the ONSTAR® system, the GPS receiver is mounted in the brick which, in turn, is mounted in the vehicle trunk or under or behind one of the seats.
As noted above, it is very difficult to install a vehicle communication and control system in a vehicle. Furthermore, the next vehicle model this system is added to is likely to require a different installation. Tooling of parts for the vehicle may have to be modified to hold the brick and the antennas. Space has to be allowed for all the wiring between the user interface, the vehicle, the audio system, the GPS antenna, the cellular antenna, and the brick. Each car may require a slightly different installation and have tooling modified and extra parts tooled to accommodate the system being added.
There exists the need for a tri-band antenna module of reduced size that can be readily incorporated within a vehicle communication and control system and may be more readily installed in a vehicle.